1. Field of the Invention
The present invention relates to an image reading apparatus and method, and more particularly to an image reading apparatus and method in which a developed photographic material is illuminated and an image recorded on the photographic material is read on the basis of light transmitted therethrough.
2. Description of the Related Art
In recent years, photographic processing methods have been proposed in which a film image recorded on a photographic material such as a developed photographic film (hereinafter referred to simply as a photographic film) is read in such a manner as to be separated into component colors of R, G and B, and image data obtained by reading the film image is subjected to image processings such as various corrections, and thereafter, an image is recorded on a recording material or is shown on a display.
Generally, in an image reading apparatus which is used to read film images in this type of photographic processing method, reading a film image on a photographic film to be read is carried out in such a manner that light is irradiated onto the film image, and light transmitted through the film image is focusd and read as image data of plural pixels by an image sensor such as a linear CCD, an area CCD, or the like, which is provided at an focusing position.
There are various types of photographic films such as negative films on which negative images are recorded, positive films (reversal films) on which positive images are recorded, and the like, and negative films and positive films greatly differ in characteristics. FIG. 14A shows an example of transmittance characteristics of a non-exposed portion of a negative film (i.e., the base of a film), while FIG. 14B shows an example of transmittance characteristics of a non-exposed portion of a positive film. As shown in FIGS. 14A and 14B, in general, the transmittance of the non-exposed portion of a negative film is increased in the order of the wavelength regions of B, G, and R, while the transmittance of the non-exposed portion of a positive film has substantially the same value for the wavelength regions of R, G, and B.
As described above, there is a great difference between the transmittance characteristics of negative films and those of positive films. Therefore, a problem exists in that, if a film image is read without correcting the difference in the transmittance characteristics, the color balance of the film image is lost and a variable range of the charge accumulation time of a CCD is used up, and as a result, color correction cannot be effected. In this case, since the signal-to-noise (S/N) ratio is low, a rough image is formed, or a dull image is formed due to color mixing. In order to realize image reading at a high S/N ratio, it is desired that the number of charges to be accumulated in the CCD be as large as possible (for example, 60% or more of saturation when a CCD of 100,000 eV is used) within a range in which no saturation of the charge accumulated in the CCD is generated.
As a technique which can be used to overcome the above problem, a technique is disclosed in Japanese Patent Application Laid-Open (JP-A) No. 6-245062. In this technique, an offset density is respectively given for the reading of R, G, and B when a photographic film is a negative film, and the same offset densities are given for the reading of R, G, and B when the photographic film is a positive film. Based on the offset densities given, adjustment of the amount of insertion of a filter which modulates (adjusts) light for reading, adjustment of the charge accumulation time by the CCD, adjustment of the amplification factor with respect to an output from the CCD, and the like are carried out.
However, in the above technique disclosed in JP-A No. 6-245062, as described above, the offset densities given for the reading of R, G, and B vary in accordance with the type of the photographic film (i.e., a negative film or a positive film). Further, adjustment of respective portions is carried out in accordance with the offset densities given. Therefore, there is a drawback in that control for varying the offset densities and adjustment of the respective portions is complicated.